The present invention is generally in connection with a power supply apparatus, and more particularly, the present invention is in connection with a power supply apparatus of simplified circuit arrangement and miniaturized magnetic element dimension.
As depicted in FIG. 1, a switching regulator which functions as a basic power supply apparatus typically comprises a power stage circuit and a voltage feedback circuit. The power stage circuit principally includes a switching circuit comprising a main transformer T1, a primary power train circuit 111, a control circuit 114 and two voltage switches Q1 and Q2. The primary power train circuit 111 is employed to receive an input voltage Vin and provides an output voltage to the primary side L11 of the main transformer T1 in accordance with an oscillating pulse signal 112. The oscillating pulse signal 112 is provided by a primary control circuit 113 which is coupled to the primary power train circuit 111 and may preferably comprise a pulse width modulation integrated circuit (PWM IC), such as 3843 or 3844 series integrated circuit chip. The control circuit 114 is used to output switch control signals to respectively control the switch operation of the on/off states of the two voltage switches Q1 and Q2, whereby rectifying the voltage at the secondary side L12 of the main transformer T1 by means of the switch operation of the two voltage switches Q1 and Q2. The power stage circuit further comprises an output low-pass filter 115, which includes an inductor 1151 and a capacitor 1152 for providing a DC (direct current) output voltage V0 to a load 110. The control circuit 114 which generates switch control signals to turn the transistor switches Q1 and Q2 on and off generally is driven by an oscillating pulse signal 119 to initialize its control function, in order that the voltage at the secondary side L12 of the main transformer T1 may be rectified in synchronization with the phase of the oscillating pulse signal 119.
Furthermore, for the purpose of stabilizing the output voltage V0 of the switching regulator, a voltage feedback circuit is required to be coupled between the output voltage V0 of the switching regulator and the input voltage Vin. The voltage feedback circuit comprises a secondary feedback control circuits 117 which detects the DC output voltage V0 and generates a voltage feedback control signal in response to the output voltage V0. The voltage feedback circuit further comprises a photo coupler 116 which is coupled in series between the secondary feedback control circuit 117 and the primary control circuit 113 for coupling the voltage feedback control signal to the primary control circuit 113 to actuate the voltage feedback control function of the primary control circuit 113. In this way, the DC output voltage V0 can be insulated from the primary side L11 and the secondary side L12 of the main transformer T1 by means of the photo coupler 116.
As explained above, in order to assure that the control circuit 114 which controls the on/off states of the voltage switches Q1 and Q2 can rectify the voltage at the secondary side L12 of the main transformer T1 to a desired voltage, an oscillating pulse signal 119 is needed to be applied to the control circuit 114 so that the control circuit 114 can rectify the voltage at the secondary side L12 of the main transformer T1 in synchronization with the phase of the oscillating pulse signal 119. The oscillating pulse signal 119 is typically transmitted from a driver transformer T2 coupled with the primary control circuit 113. The primary side of the driver transformer T2 receives an oscillating pulse signal from the primary control circuit 113, and at the same time an equivalent oscillating pulse signal 119 is induced on the secondary side of the driver transformer T2. The induced oscillating signal 119 acts as a driving signal to drive the control circuit 114 to rectify the voltage at the secondary side L12 of the main transformer T1 by means of the switch operations of the voltage switches Q1 and Q2.
Still referring to FIG. 1, in order to startup the control function of the secondary feedback control circuit 117, an external auxiliary power source 118 is required to be connected to the secondary feedback control circuit 118 to provide sufficient power to initialize the secondary feedback control circuit 117. FIG. 2, FIG. 3 and FIG. 4 illustrate several modified circuit configurations of the switching regulator of FIG. 1. In FIG. 4, the photo coupler which is employed to isolate the DC output voltage V0 of the switching regulator from the primary side L11 and the secondary side L12 of the main transformer T1 is removed from the voltage feedback circuit, and a magnetic element T3 is coupled between the primary control circuit 113 and the secondary feedback control circuit 117 for coupling the voltage feedback control signal from the secondary feedback control circuit 117 to the primary control circuit 113. A rectifier circuit 20 is further coupled in series between the magnetic element T3 and the secondary feedback control circuit 117 for rectifying the voltage induced at the secondary side of the magnetic element T3 into a DC voltage, and the rectified DC voltage is taken as the auxiliary power source for operating the secondary feedback control circuit 117.
Nonetheless, the performance of the photo coupler 116 is susceptible to the ambient temperature and incident light beam, and thus the mean time before value (MTBF) of the conventional power supply apparatus will get worsened gradually. In addition, the number of the magnetic elements in the power supply apparatus is a decisive factor for the size of the power supply apparatus. The more magnetic elements presented in a power supply apparatus, the larger size the power supply apparatus will occupy. Moreover, the large number of the magnetic elements in a power supply apparatus implicitly indicates that the circuit arrangement of the power supply apparatus will be much complicated, which might become a handicap of designing the power supply apparatus to fit the requirements of compactness and low-cost.
There is a tendency to look for a way to integrate the functionalities of driving the control circuit at the secondary side of the main transformer to carry out synchronous rectification, coupling the voltage feedback control signal to the control circuit at the primary side of the transformer, and providing the auxiliary power required to operate the feedback control circuit of the voltage feedback circuit, into an unitary magnetic element for use in a power supply apparatus.
In accordance with one aspect of the present invention, a power supply apparatus for regulating an input voltage to provide an output voltage to a load is provided and comprises a power stage circuit including a switching circuit for receiving and rectifying an input voltage and an output filter for providing an output voltage to a load, and a voltage feedback circuit coupled between the output voltage and the input voltage, wherein the voltage feedback circuit includes a feedback control circuit for detecting the output voltage and outputting a voltage feedback control signal in response to the output voltage, a control circuit for outputting a first oscillating signal to the switching circuit, a magnetic element coupled in series between the feedback control circuit and the control circuit for receiving a second oscillating signal from the control circuit and coupling the second oscillating signal to the switching circuit and coupling the voltage feedback control signal to the control circuit, and a rectifier circuit coupled in series between the feedback control circuit and the magnetic element for rectifying the second oscillating signal into an auxiliary voltage for operating the feedback control circuit.
The switching circuit may further comprises a main transformer, a first power train circuit coupled to the primary side of the main transformer and a second power train circuit coupled to the secondary side of the main transformer. Further, the load in accordance with a preferred embodiment of the present invention at least includes a capacitor. Also, in a preferred aspect of the present invention, both the first oscillating signal and the second oscillating signal are directed to an oscillating pulse signal. The first oscillating signal is applied to drive the first power train circuit to regulate the input voltage to provide a voltage to the primary side of the main transformer, and the second oscillating signal is applied to synchronize with the secondary power train circuit to rectify the voltage at the secondary side of the main transformer.
Now the other objects, the foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the accompanying drawings, wherein: